1. Field of Invention
The invention relates to an antenna, and more specifically to an antenna with a vertical complementary fractal structure.
2. Related Art
With the rapid development of wireless communication and semiconductor technology, wireless communication has become an indispensable part of life. A wireless communication system is comprised of a transmitter/receiver and antennas, wherein the antennas are used to convert electrical energy into electromagnetic energy or vice versa. This is one of most important components in communication systems. Given the demand for the miniaturization and multi-band capability of electronic devices, the current trend of antenna design is towards miniaturization, structural simplification, and multi-band or wide-band capability.
Many existing studies have focused on microstrip antennas and array antennas. In general, microstrip antennas have the advantages of being easy to produce, small in size, light weight, and low profile. However, they also have the problems of low radiation efficiency and narrow band.
Another type of antenna under development is the fractal antenna. By drawing upon electromagnetic theory, the concept of the fractal structure has been successfully applied to issues related to electromagnetic radiation, transmission, and scattering field. Because of their characteristic of self-similarity, fractal antennas are characterized by unlimited bandwidth. Thus the development of fractal antennas has received increasing attention.
At present, there are two kinds of applications of the fractal structure: one is to directly use existing fractals and the other is to develop new fractal structures based on the characteristic of self-similarity of fractals. By incorporating the array fractal antennas to microstrip antennas, the problems of microstrip antennas may be overcome with the multi-band capability and high gain of fractal antennas.
The relevant prior art discloses a fractal antenna, and the main idea of the fractal antenna is to change the shapes of the holes of the ground connection plane to control the radiation efficiency. See, for example, Ban-Leong Ooi, “A Modified Contour Integral Analysis for Sierpinski Fractal Carpet Antennas With and Without Electromagnetic Band Gap Ground Plane”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 5, MAY 2004.
U.S. Pat. No. 6,127,977 discloses a fractal antenna using a two-layer fractal structure to increase bandwidth and radiation efficiency. U.S. Pat. No. 6,642,898 discloses a fractal cross slot antenna using cross slots with a linear fractal structure instead of conventional non-fractal cross slots. The type of fractal antenna disclosed in U.S. Pat. No. 6,476,766 achieves its compact design by staggering the slot structures at the upper level and lower level.
Reducing the size of antennas has always been an important objective of the field. In general, antennas without consideration of the ground connection plane design are of a larger size. Antennas with a ground connection design are of a smaller size; however, they occupy a large area of ground and space. Because fractal antennas are a type of newly-developed antenna that have attracted a great deal of attention, it is often thought that certain characteristics of fractal antennas are helpful to reduce the size, increase the bandwidth, and to improve the radiation field of the antennas. However, in practical use, in order to achieve higher radiation efficiency, fractal antennas usually do not adopt a ground connection plane. The prior art does not disclose any fractal antennas having a ground connection design.